Neoproterozoic eclogites in the Paleoproterozoic Ubendian Belt of Tanzania: Evidence for a Pan-African suture between the Bangweulu Block and the Tanzania Craton

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• 作者：Nelson Boniface^a ; ^{nelson.boniface@udsm.ac.tz} ; Volker Schenk^b ; ^{vs@min.uni-kiel.de}
• 关键词：Eclogite ; Pan-African ; Ubendian Belt ; Tanzania Craton ; Bangweulu Block ; Gondwana
• 刊名：Precambrian Research
• 出版年：2012
• 期刊代码：75_03019268
• 类别：ear
• 出版时间：July, 2012
• 卷：208-211
• 期：Complete
• 页码：72-89
• 文件大小：2844 K

摘要

Geochronological, petrographic and geochemical data from eclogites of the Ufipa Terrane in the Ubendian Belt demonstrate that a Pan-African suture zone dated at , and  Ma (zircon U-Pb SHRIMP) separates the Tanzania Craton from the Bangweulu Block along the Ubendian Belt. These new and surprising data indicate that during the amalgamation of the Gondwana Supercontinent there was a collision between the Archean Cratons of Tanzania and Bangweulu. A clockwise P-T path that climaxed at pressures of 15-20 kbar and temperatures of 610-790 C were estimated for these eclogites. This indicates a relatively warm subduction with a geothermal gradient of about 10-11 C/km.

Magmatic precursor rocks of kyanite-free eclogites crystallized in the back-arc (group I eclogite) and island-arc (group II eclogite) tectonic settings. The light rare earth elements (LREEs) of group I eclogites range between 10 and 30 times chondritic values suggesting a depleted mantle source similar to that of mid oceanic ridge basalts (MORB). Group II eclogites display characteristic depletions of high-field-strength elements (Na, Ta, Zr and Hf) relative to LREEs that is typical for island-arc basalts.

The U-Pb zircon ages at and  Ma from the kyanite-free eclogites have a difference of about 70 Ma. The time interval of this much long is not likely to represent a single subduction event. Therefore, it is more likely that successive accretions of volcanic-arc rocks occurred at , and  Ma.